Koller Formenbau GmbH discovered for itself the advantages of Parabolic Performance Cutting (PPC) from the Hoffmann Group. With PPC, Koller has not only reduced the finishing operation time for tool molds and mold plates by 85 percent, it has also improved the surface quality.

In the tranquil Altmühltal, between Ingolstadt and Nuremberg, Koller Formenbau GmbH develops and manufactures tools, injection tools and lightweight components. Their principal customer is the automobile industry. Tailor-made solutions from Koller are held in great regard by virtually all automobile manufacturers. When in summer 2017 the company was optimising its electrode manufacturing facilities, the programmers using the CAD/CAM suite hyperMILL from the software house OPEN MIND noticed the optional performance package hyperMILL MAXX Machining. The innovative strategies offered in that package promised substantial savings in finish machining of tool molds and press plates made of tool steel, and irresistibly attracted attention. Markus Ferstl, Department Manager for Mechanical Machining/CAM, therefore resolved to put the new procedure to the test immediately. However, procurement of the tools necessary for this finish machining process proved to be no simple matter, and the first tests failed to yield the desired results. Then Ferstl found that the Hoffmann Group were currently in the process of launching barrel milling cutters on to the market under the Garant brand name.

From the exhibition straight on to the machine

We had already been customers of the Hoffmann Group for many years. But still I was somewhat surprised to learn that the Hoffmann Group were offering such complex tools under the Garant brand name”, recalls Ferstl. By now, time was pressing, since the scheduling of the production changeover would admit no further delays. Ferstl immediately contacted his contact person at the Hoffmann Group, the application technician Harald Näcker. Näcker had himself worked as a machinist for more than 20 years before he joined the Hoffmann Group, and had been involved in supporting Koller Formenbau GmbH for 18 years, so he knew the company very well. However, he could not help spontaneously because the brand new Garant PPC milling cutters were required at that time to celebrate their world première at EMO 2017, the leading international exhibition, and could not be retrieved. But as soon as the milling cutters were available, Näcker was knocking on Koller’s door with the sought-after tools in his hand. “For us every minute counted”, adds Ferstl. “So, we didn’t test them very long, we put them straight into production. Of course, OPEN MIND and the Hoffmann Group had guaranteed that the concept was fully proven, with extremely high process reliability – and we knew from experience that we could rely absolutely on the statements of both partners.”

Shorter process times for complex geometries

But what is it that makes PPC milling quite so attractive? Parabolic Performance Cutting (PPC), also known as barrel milling, is a further development of the application of ball-nosed slot drills. The main cutting edge of PPC milling cutters is curved, as an arc of a larger radius circle. In comparison to ball-nosed slot drills of the same diameter, PPC milling cutters have a significantly larger effective radius and a greater engagement length. This results in a 9-fold increase in the line skip for the same surface quality. If on the other hand the same line skip is maintained, a surface quality up to 80 times better can be achieved. To fully exploit the advantages of PPC, the tool must also be matched as closely as possible to the demands of the workpiece surface that is to be machined. GARANT PPC milling cutters are therefore available with an effective radius of 250 to 1000 millimetres and in four basic profiles: straight, tangential, conical and stub point conical. In addition, tools with the same effective radius and diameter but different approach angles are available. That is helpful for programming and where access is difficult.

85 % shorter machining time

At Koller Formenbau, where the ruled surfaces to be finish machined constitute up to 75 percent of the total area of the mold, conical Garant PPC milling cutters with an effective radius of 1000 millimetres are used. The corners of the molds are easily machined using the tips of the PPC milling cutters. “Our PPC milling cutters have a very special geometry, and the profile is currently not available from any other manufacturer” is how Harald Näcker describes the special features of the PPC milling cutters which form part of the Garant high-end product range. Koller Formenbau now uses exclusively PPC milling cutters for finish machining ruled surfaces, since the results are unbeatable: “Using Garant PPC milling cutters, machining the tooling frame now takes only 15 hours instead of 100”, reports Ferstl with pleasure. “We had not expected that such large jumps in performance would be possible in this day and age; and in saying that I am referring not only to the milling speed but also to the dimensional accuracy. The tolerances we now must allow are never more than 1/100 millimetres. The enormously efficient hyperMILL MAXX Machining finishing strategies and GARANT PPC barrel milling cutters have released valuable machine hours which we are already putting to intensive use on other jobs. For us, that’s what counts. We don’t mind the tools being rather more expensive if they pay for themselves quickly. Therefore, the PPC milling cutters are currently running on all our machines and in future will also be used in China.” So that they can serve their Chinese customers better, from 2019 Koller Formenbau are opening their own production workshop in China. This will be an ultra-modern factory built on a property of 50,000 square metres close to Shanghai, for series production of automobile parts including tool shop, and subsequently a development centre for lightweight components. By the end of 2018, 15,000 square metres of workshop and office areas will have been built. In the first quarter of 2019, machine tools and series production equipment will be installed, and from September 2019 series production of automobile parts will start. Especially when it comes to major orders, the production sites at Dietfurt and Nanjing will cooperate closely, to the benefit of customers throughout the world.

Best results with 2 to 3 axes

Contrary to generally recommended procedures, Koller Formenbau operates the PPC milling cutters not in 5-axis mode but in 2-axis to 3-axis mode. “What matters above all is that the machine drives the tool”, is Ferstl’s logic for this procedure. “Therefore, we use only the X, Y and Z axis, and clamp the others out of use. That stabilises the process and protects the machines.” Koller is also very pleased with the tool life achieved by the PPC milling cutters. Finish machining of a geometrically defined surface now requires only 2 different tools, and the surfaces are of higher quality than before. “The Garant PPC milling cutters were a real lucky break for us, and we are already looking forward to the next big innovation from the Hoffmann Group. That’s because we know that from time to time new jumps in performance can happen”, summarises Markus Ferstl.

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